1. Field of the Invention
This invention relates to a hydrocarbon conversion process for reducing the pour point of a distillate having a boiling range above about 320.degree. F. More particularly, it relates to a process for reducing the pour point of a catalytically cracked light cycle oil. This invention especially relates to the catalytic hydrodewaxing of a catalytically cracked light cycle oil.
2. Description of the Prior Art
Middle distillates obtained from crude oil, such as gas oils, have been processed heretofore to produce fuel oil products, including home heating oil, diesel fuel, furnace oil and the like. Specifications for these products normally include a requirement that the pour point may not exceed a certain maximum value. In some instances it is necessary to subject these distillate fuels to additional processing whose principal purpose is to reduce the pour point of the feedstream.
One such process, developed heretofore, is referred to as catalytic hydrodewaxing in which gas oil is contacted with hydrogen and a shape selective catalyst adapted to selectively crack or hydrocrack the paraffinic molecules in the gas oil. Initially the catalysts used were those zeolite cracking catalysts which had pore openings sized so that they would admit and crack only normal paraffins and exclude all other gas oil components, e.g. erionite type zeolite. U.S. Pat. No. Re. 28,398 of Chen et al. discloses an improvement to this process through substituting ZSM-5 type of zeolite for the previously used erionite type cracking catalyst. Using this type catalyst permitted more efficient operation. In addition to the normal paraffins, paraffins with slight branching e.g. with a methyl side group, were also cracked whereby dewaxing was carried out to a greater extent. This permitted lowering of the gas oil pour point in a very efficient manner. The product of hydrodewaxing gas oil may be suitably fractionated to produce high yields of dewaxed gas oil boiling in the same range as the feed, some naphtha and some light (C.sub.4.sup.-) ends.
Catalytic dewaxing with a ZSM-5 type zeolite may be employed to improve the quality of a variety of feedstocks. In addition to gas oil, Chen et al.'s reissue patent discloses other useful feedstocks including crude oil, full range dehydrated shale oil and lube oil stock. U.S. Pat. Nos. 3,893,906 and 3,894,939 of Garwood et al. disclose that a mixture of gas oil and aromatic naphtha will yield a low pour point gas oil and a higher octane gasoline when subjected to this catalytic hydrodewaxing while U.S. Pat. No. 3,989,617 of Yan discloses an improvement process for catalytically treating lubricating oil base stocks with ZSM-5 type zeolites. Other improvements in this process when used alone or in combination with other processes are disclosed in U.S. Pat. Nos. 3,755,145 of Orkin, 3,852,189 of Chen et al., 3,894,938 of Gorring et al. and 3,956,102 of Chen et al.
One particularly effective combination process of catalytic cracking and catalytic hydrowaxing is disclosed in U.S. Pat. No. 3,891,540 of Demmel et al. This process is concerned with producing a light fuel oil with a low pour point. The catalytic cracking employs relatively mild conversion conditions, i.e. 45 volume percent, of fresh gas oil and heavy cycle oil in one riser and intermediate cycle oil in the second riser. The light cycle oil recovered from the catalytic cracking fractionator is subjected to catalytic hydrodewaxing with a ZSM-5 type crystalline zeolite. The effluent from the hydrodewaxing reactor is condensed, the hydrogen recovered for recycle and the condensed light sent to the hydrodewaxing unit fractionator. Here the desired low pour point fuel oil is recovered as the bottoms with the tower overhead of about 400.degree. F. minus hydrocarbons comprising C.sub.4 and lighter gaseous products plus hydrocarbons in the gasoline boiling range. The combination process of Demmel et al is practiced in two complete processing units, a catalytic cracker with all its usual attendant equipment, including a fractionator and a catalytic hydrodewaxer with its usual attendant equipment, including a fractionator. Thus, these units may be operated in combination or separately in a blocked-out operation.
It is an object of this invention to provide a process for reducing the pour point of catalytically cracked light cycle oil.
It is another object of this invention to provide a process for reducing the pour point of catalytic cracked light cycle oil which is integrated with the operation of the catalytic cracking unit.
It is a further object of this invention to provide a hydrodewaxing process integrated with a catalytic cracking process so as to perform the combined processes in a simpler fashion or by a reduced number of steps than is required for the individual processes.